/*
 * Copyright (c) 2000-2011 ymnk, JCraft,Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this list of conditions
 * and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
 * conditions and the following disclaimer in the documentation and/or other materials provided with
 * the distribution.
 *
 * 3. The names of the authors may not be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL JCRAFT, INC. OR ANY CONTRIBUTORS TO THIS SOFTWARE BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * This program is based on zlib-1.1.3, so all credit should go authors Jean-loup
 * Gailly(jloup@gzip.org) and Mark Adler(madler@alumni.caltech.edu) and contributors of zlib.
 */

package com.jcraft.jsch.jzlib;

final class Adler32 implements Checksum {

  // largest prime smaller than 65536
  private static final int BASE = 65521;
  // NMAX is the largest n such that 255n(n+1)/2 + (n+1)(BASE-1) <= 2^32-1
  private static final int NMAX = 5552;

  private long s1 = 1L;
  private long s2 = 0L;

  @Override
  public void reset(long init) {
    s1 = init & 0xffff;
    s2 = (init >> 16) & 0xffff;
  }

  @Override
  public void reset() {
    s1 = 1L;
    s2 = 0L;
  }

  @Override
  public long getValue() {
    return ((s2 << 16) | s1);
  }

  @Override
  public void update(byte[] buf, int index, int len) {

    if (len == 1) {
      s1 += buf[index++] & 0xff;
      s2 += s1;
      s1 %= BASE;
      s2 %= BASE;
      return;
    }

    int len1 = len / NMAX;
    int len2 = len % NMAX;
    while (len1-- > 0) {
      int k = NMAX;
      len -= k;
      while (k-- > 0) {
        s1 += buf[index++] & 0xff;
        s2 += s1;
      }
      s1 %= BASE;
      s2 %= BASE;
    }

    int k = len2;
    len -= k;
    while (k-- > 0) {
      s1 += buf[index++] & 0xff;
      s2 += s1;
    }
    s1 %= BASE;
    s2 %= BASE;
  }

  @Override
  public Adler32 copy() {
    Adler32 foo = new Adler32();
    foo.s1 = this.s1;
    foo.s2 = this.s2;
    return foo;
  }

  // The following logic has come from zlib.1.2.
  static long combine(long adler1, long adler2, long len2) {
    long BASEL = (long) BASE;
    long sum1;
    long sum2;
    long rem; // unsigned int

    rem = len2 % BASEL;
    sum1 = adler1 & 0xffffL;
    sum2 = rem * sum1;
    sum2 %= BASEL; // MOD(sum2);
    sum1 += (adler2 & 0xffffL) + BASEL - 1;
    sum2 += ((adler1 >> 16) & 0xffffL) + ((adler2 >> 16) & 0xffffL) + BASEL - rem;
    if (sum1 >= BASEL)
      sum1 -= BASEL;
    if (sum1 >= BASEL)
      sum1 -= BASEL;
    if (sum2 >= (BASEL << 1))
      sum2 -= (BASEL << 1);
    if (sum2 >= BASEL)
      sum2 -= BASEL;
    return sum1 | (sum2 << 16);
  }

  /*
   * private java.util.zip.Adler32 adler=new java.util.zip.Adler32(); void update(byte[] buf, int
   * index, int len){ if(buf==null) {adler.reset();} else{adler.update(buf, index, len);} } void
   * reset(){ adler.reset(); } void reset(long init){ if(init==1L){ adler.reset(); } else{
   * System.err.println("unsupported operation"); } } long getValue(){ return adler.getValue(); }
   */
}
